1. Field of the Disclosure
The present disclosure generally relates to store-to-load forwarding for processors.
2. Description of the Related Art
Processors typically enhance processing efficiency by employing out-of-order execution, whereby instructions are executed in an order different from the instructions' program order. In order to avoid errors, a processor executing instructions out of order uses memory disambiguation techniques to account for dependencies between load and store instructions. One such memory disambiguation technique is to delay committing store instructions (e.g. writing store data to the processor cache) until the store instructions are ready to be retired. The store instructions, including their respective store data, are maintained in a store buffer until retirement. Using a technique referred to as store-to-load forwarding, a load instruction that is dependent on a store instruction in the store queue is satisfied by providing the store data from a target register of the store instruction, so that the load instruction does not retrieve incorrect data from the cache.
In some cases, the processor can mistakenly identify a load instruction as dependent on a particular store instruction, resulting in incorrect data being forwarded to the load instruction. A mistaken store-to-load forward typically is addressed by either replaying the load instruction so that it receives correct data or, if the load instruction is past the point in an instruction pipeline where it can be replayed, via a resynchronization, or resync, operation whereby the processor state is synchronized to state data saved prior to the mistake. Such resynchronization operations can have a substantial impact on processor performance. Further, because mistaken store-to-load forwards can cause catastrophic errors if left unaddressed, processors typically take a conservative approach whereby a resync operation is performed if the correctness of a store-to-load forward cannot be verified.
The use of the same reference symbols in different drawings indicates similar or identical items.